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I think schraders suck as pilots in general, a larger area wouldn't be that much force push, schraders are pretty easy anyways, it will be less a blowgun,

with my experience in using mini pneumatics, pistons like to get stuck in their position, commercial application almost always use diaphragm based designs over pistons and they hardly need to be replaced

iknowmy3tables wrote:with my experience in using mini pneumatics, pistons like to get stuck in their position, commercial application almost always use diaphragm based designs over pistons and they hardly need to be replaced

I've probably made more mini-piston launchers than anything else and in my experience if made well they're very reliable.

jackssmirkingrevenge wrote: I prefer to use "conventional" short projectiles like pellets and cut down on the pilot volume, here's a design I've been pondering with a solid rubber piston. The pilot volume is increased (no, I'm not high or anything ) but this should be offset by the fact that dead space is almost zero compared to the original design.

I'd always assumed in your other design further up the page that the projectile would be just in front of the piston (and have next to no deadspace) like a standard coaxial.

SPG wrote:I'd always assumed in your other design further up the page that the projectile would be just in front of the piston (and have next to no deadspace) like a standard coaxial.

I figured the projectile would be at the mouth of the cartridge, the thought of it having already accelerated before jumping the gap between cartridge and barrel led to visions of shattered breeches that I wasn't comfortable with, however if everything is aligned there's no reason why that shouldn't work.

I just got a quote for the screw attachment for the burst disk, 12 euros - not terribly expensive but that works out at 120 euros (around $180 US for those across the pond) for the 10 cartridge batch I was planning. Nothing I can't afford, but the power had better be worth it. I'll have one made for now to see what sort of potential the idea has and move from there. Piston cartridges would be cheaper, but involve a lot more work to make and are more prone to failure, while the burst disk would have no moving parts.

Same coaxial design but with a simpler design using a solid rubber piston and taking advantage of having HPA on tap. I have 9mm I/D brass tubing that will make a good body for the cartridge, it should make it easy to keep things concentric and I'm going to try and use the higher strength blue Araldite instead of my usual marine epoxy. At around 3" overall length and 3/8" diameter it will be smaller than a loaded 0.303" rifle cartridge, so in terms of "realism" it should be spot on. GGDT predicts reasonable power at 800 psi, and hopefully there will be enough power to cycle a straight blowback mechanism.

If it works, I hope to make something looking like a cut down rifle, along the lines of the M1 Garand from Hellsing (here's looking at you, Brian )

I know, long time no type. I got sidetracked into building up a Citroen 2CV 4x4 (and thank god given the snow falling outside, and also a plywood canoe and a couple of longbows. Oh and a woman may have had something to do with it to.

Instead of adding sealing discs, I cut masking tape into thin strips and rolled it around to make sure things remained centred. Sorry about the poor quality photos, my digital camera's buggered and I'm using my cellhpone.

Also... Is the barrel the piece on the left?

It seems to big but maybe i'm just not scaling it right in my head

Yes, the body is 9mm I/D and the "barrel" is 5.5mm I/D.

Here's the finished article next to a 0.303" rifle cartridge for comparison: